Reversible propeller



2 SHEETS-SHEET l Filed Jan. 2, 1947 lhmentor April 14, 1953 w. w. FRANK REVERSIBLE PROPELLER 2 SHEETS-SHEET 2 Filed Jaxl. 2, 1947 Patented Apr. 14, 1953 2,634,815 i REVER SBLE PROPELLER Wilbert W. Frank, Packanack Lake, N; J., assignorl to Curtiss-Wright Corporation, a

of Delaware corporation Application January 2, 1947, serrano'. 719,335

This invention relates to a reversiblefpitchA aircraft Apropeller and control mechanism for.

eiecting fast pitch reversal and providing speed.A

governing in both forward and reverse pitch.

Forthe purpose of improving the maneuverabilityof aircraft upon landing, the prime mover is adapted to function as a power brake by reversing thev pitch of the propeller blades. In such systems, it is usual to reverse the propellers to a fixed reverse pitch limit and vary the aerodynamic braking effect through throttle control of` the prime mover. In such systems, the rate of changing the pitch from forward to reverse has been relatively slow and requires the attention of the operator through throttle control to regulate the braking effect. The use of a fixed pitch limit in reverse pitch in combination with throttle control for varying the braking thrust is a matter of expedience since a small change in pitch of a propeller when in the reverse pitch range results in excessive changes in the torque load placed upon the prime mover, so that if a pilot were to vary the pitch to vary braking effect there would be danger of stalling the prime mover. In effecting a change of pitch from forward pitch through ilat pitch to reverse pitch, there also exists some danger of over-speeding of the prime mover since when the propeller pitch is reduced to zero the prime mover load is momentarily reduced to zero, and any substantial delay encountered in passing through zero pitch would produce a sudden over-speeding condition of the engine, should the pilot fail to close the throttle.

While governing the speed of a prime mover when in reverse pitch has been suggested by varying the pitch "of the blades, extreme diiculty would be encountered because of the great load change sensitivity of the propeller to extremely small changes in pitch when in the reverse range. Unless provision can be made to attain reverse pitch before over-speeding can occur, it has been found desirable to provide a system wherein the engine throttle is first closed while the propeller traverses the zero pitch region. Any momentary closing of the throttle interrupts the continuous flow of power from the prime mover and is bound to delay for adefinite period the time which must elapse before the reverse pitch can be effective to produce a maximum braking effect. Thus while reverse pitch has been employed in the manner'set-forth above for assisting in the landing'of aircraft, it will be realized that during landing operations the speed of the aircraft is considerably reduced and the time required for actual development of reverse thrust need not 1o claims; (o1. 170g- 160m be in the order of asplit second; as would be desirable for braking power@ dives at high speed and for acrobaties generally.

It is accordingly anv object of the :present in.y vention to provide a reverse pitch mechanism, for an aircraft propeller in which reversal of.,

pitch may be attained at such a high rate as to substantially eliminate danger of prime mover over-speeding during such reversal.

Another object of the invention is to provide in a propeller v`engine Acombination wherein.

through pitch variation of the propeller constant speed is maintained, a means for quickly reversing. the pitch and the sense of the governor whereby constant speed control is substantially continuously maintained.

Still another object of the invention is to provide a propeller system capable of operating to maintain constant speed when either in forward or reverse pitch, with the rate of pitch variation when in reverse pitch substantially reduced to compensate vfor the increased load sensitivity of the propeller topitch changes in the reverse pitch range. l y

Still another object of the invention is to provide in a propeller governor system in which the pitch of the propeller may be reversed, a mechanism for rapidly reversing the propeller pitch to within a desired range and thereafter establishing governor control over the pitch.

Yet another-object of the invention is to provide a reversible pitch propeller and governor combination in which the propeller may normally vary within a range of forward pitch to lcontrol propeller speed and Vary within a range of reverse pitch at a substantially decreased rate to control propeller speed and in which the pitch of the propeller may be quickly changed independent of governor control from within one range to a position ywell within the other range whereupon governor control is restored.

The above and other novel features of the invention will appear more fully hereinafter from the following detailed description when taken in conjunction with the accompanying drawings. It is expressly understood, however, that the drawings are employed for purposes of illustration only and are not designed as a definition of the limits of the invention, reference being had for this purpose to the appended claims.

In the drawings wherein like reference characters indicate like parts,

Figure 1 is a circuit diagram illustrating the control system as applied to an electric variable pitch propeller.

ranges of blade pitch angle which may be estabalished by the cam arrangement of Figure 3, and employed in the operation of the system?4 Referring to Figure 1, there isdiagrammaticals.-

ly shown a reversible electricepitchgchanginggmow-15g.

tor I0, having an armature I2, reverse and forward iields I4 and I6, commutatonlanclaseries.

electromagnetic release frictizrrbrakefofwell't known type generally indicated by therbrakeccoir.

I9 for holding the propeller in fixed pitch when desenergizecland .no.,change..of `pitch required.V SiclLa vmot'or., mayJ b'e. rotatablyl carri'edby, the., propeller and "'act' through. aplanetary. or lother gear. reduction. .system itoi. 'alter the; pitelipof `tli'e" blades, for.' example in" theA manner shown. in Blanchard 1,951,320 or Palmer.. andi' McNeil 2124078f Pwerfor' actuatingvtne `motor: I IVmayjbe."de'L rivedfrom a battery"20,` orreiside ofzwhichis" grounded at 2 I; ,andtthe othersi'deiofwhichtis" connectedtoab'atterypotential bus .22'. Ir'orderv toA provide momentarily an `increase inpotential i torenforc'e rapid"acceleration"andi'high speed'op; erationoftli'e'motorrl 0j" avoltagebo'oster 'Zilfmay beprovidedto establish highefpotential in the" voltage boosterbus' 265 To-provide-'governorcontrol over the pitch of the pro-pe1ler"b1adessoas tti-:maintain a desiredconstant:speed a' governor 28V is* provided` in which increase-and" decrease pitch" contactera() and` 32"*respectivel5'fr are-proivided lsuch `that upon" an` increase inspeed'above that* desired; the Yintererxgaging contactl 3II`l is mad'ecto close acircuit"through4 contact"3ll` and upon: la decrease-in speed'fismade tocl'ose `a-` simi-'- lar circuit through contact 32. mayco-rrespond" tof-thecgovernor shownin' al copending applicationof- Charles Chillsonl'ed" March-'15, A193gurrde-rSerial No.'-26-I',`8.791,'fnow Pat#y ent-f No.'J 2,4495452? I orderV4 to# determine and" limit the normal-j 50 range of movement foffthe #propeller blades; limit switches 36 and 138aref1-provide`dand are=so connectedA as. to :function:for'thefpurpose-specidin? connection-A with b'oth. the normal rangefloff-pitchlf tofbeaestabli'shedj and aerange*off'reversefpitclitofv bee'estalsilislieclf.`A Tritransixerringffrom;onefrange'5 te ithesother; additional Eli'init 4switches-1l and"4 21' are provided-sof that as lthe: propeller4 pitch? ap'- l proachesforfattains :the reverseiloifnormal range" otfpitchf variation idesied operation 'off thel :pitch cha-nge motor isfcausedftolbearrested Thef'li'mit' switch 46 for eXa-mplerisf-adapted tof initiate-'the'- arresting.2 of" thec pitch" change motor in or as it approachessthe'.reverse pitch range` Whereasffth'e* limitswitch1v42 fistadap-t'ed to. initiate arresting of.

the motor-'atfa;selectedrfpositionv withinIthe-.normal .S or positive pitch' ranger.

Referringto 'Figuress2fand.3, itiwill.,beflseensthatzv theelimitfswitches 36;: .38; ..40 f'an'd 142 f. are: cam op;

erat'ediby suitablyrfdisp'osedf camsmounted.l upon'. 70

the output shaftM'of LtherpOWerLun'it; 'Dheshaft 44:z'isgearedzdirectlyvthrouglr'almastergear"46ste each blade gear 48 carried uporrthee'rootuendofd each ofifth'efpropeller" blade: Shanks z 50i Itf'will bezappreciated thatzthe propellerrbladefismounts ed within an integral hub socket 52?:andretained;

'I 'he governor* therein by centrifugal load carrying anti-friction bearings '54 and a preload bearing 55 held in place by a threaded retaining ring 56. The master gear 46 is rotatably supported upon an anti-friction bearing 58 located in a bulk head 60 secured to the hub 52. The master gear 46 is splned to the power output sleeve 413 which carriescthereonfarsplinedsdouhlefanged ring 62 having spaced:1ianges sandiladaptedto carry switch operating cams. The spline shaft 44 is driven from a suitable gear reduction unit IU from the electric motor diagrammatically shown at-IIli-inFigure l. Located about the cam ring 62sandssecuredswithin the housing -63 are limit swtchesldQSB'f and 42, four in all, arranged at 90" intervalseaboutthe cam ring 62. Each of the switchesareactuated by cam followers 16, 18, andc 2;eachractuate'd by oneA or more of the cams 35,1511x 35, 4I, 43 and 45 such that upon the cam followers being lifted radially outwardly by their respectiveccams, the circuit .withinthe switchis broken.v The cams yare'securedtothe camring ilanges' tiand "68;b'yjbo1ts 94located intheiholes in the flangesggthe" latter providing suitable'am gular position adjustment;

Referring to the circuit lof Figurel; in moredetaiL' itiwill be seen" thatthebattery" potential busY 2 2; is normal-ly connectedv through the closed'lcon; ta'cts^ I 63 and'`T I U2 of' manual fast reverse and' fast returntomorma'l switches' I 04`and I IJG'fre-nd spectivelmto amanual selectorswitch' |08; adaptecl-r to -connectthebattery forl manual pitchl in;`v` crease `orrdecreasethrough contacts "I I Il and-1 I *|251 respectively; or 'for automatic governorcontrol through contact' I I dfconnected to theV contacts off' ther governor" controlled increase and* decrease pitclrrela-ys `I I6 fand I I8 respectively: Thel operating coils of the-relays i I6'and`l I Bare-excited"- upon contact -offthefgovernor contact 34 with-oneorthe o-ther='ofcontacts 30'Jandi32`, when the'gov'- erno'r-'safetyi contacts rI2!! -are closed;Y and an -in` terrupterfrelayI vvl 22 and. time delay-relay I 24-v are f deeriergized,Y so as to'complete "a l"circuitbetween: sl'ectorswitclifcontact 1I I and a Lsuitablelground I 6.

Itis `desirab1le to: eitect substantially uniformiv increments of pitch.;z change:wv either direction; formaintaining'constant speed through governor.- control; However; the.; centrifugal twisting'mo.: mentfoftherloladeszrresistsV increases in'v pitch,A and? assists'.V4 decreasesi- 1 ordinarily". causing: the: motor lI2.' to operatevat dinerent speedsdependJ-L- ingff oni` directionn. Inrthisg.inventionzthe blades.

areprovidediwitli; counterW'ei-ghts cto. .compensates` tween :thefzmotor I 2iy and;v ther propeller v:blades` isf of relatively ilow'ratio:. ToA lobtain desired' ratesr of. pitch` change: for." normal governing, along..v

with.l high; torque;v it'l is therefore. desirable. to.'Y increasetheia motoriield strengthf while=still. usingizthe: normal voltage available from the: power: sourcefZI. As iwillb'ecome clear, the 110W-v ratiofvsp'eed'`A reduceris neededpto enable' high-v. ratesi of: pitch change ati' boosted'. voltage` in'. making ,transitionsifrom `normal to reverse.; pitch arrdivice'A versa; Means lare`- therefore' provided'l taincrea'sefthe' Aileld'.strength'rof the motor when' normally# increasing' and.v decreasing pitch, to. lower :the speed' of .the motor", through the ff'u'se. of-circuitxcmpleting retarderw relays I28 and I3Il;'1which` are adapted when the pitch. changemotorischanging pitch, to'V connect the@ dead" motorxeldfwinding in parallel withith'e armature" andfztoflfgroundzlBZ :throught a rsuitabletseries low resistance |34. For example, when relay I|8 is closed, calling for a decrease in pitch, the motor I is energized through field I4, and the series coil of the relay |30 is energized closing the contacts thereof and connecting field I6 to ground through resistor |34. The current ow in eld I4 is thus increased since the field I6 andI armature I2 both provide parallel paths of flow to ground, and since current is flowing in the field I blades are' in the reverse pitch range, the direction of rotation of the pitch change motor must be changed to effect, for example an increase in reverse pitch while traveling in a diinthe normal range and similarly to effect a decrease in reverse pitch while oppositely travel-v ing. To reverse the connections suitably, a reversing relay switch |36 is provided, actuated to normal position (as shown) or reverse position by relay coils |38 and |40, respectively. The switch may be of the latch-in or snapover type so that upon momentary energization of either coil |38 or |40, the switch is actuated accordingly and held until the other coil is energized. In the position shown, contacts |42 and |44 complete proper circuits to the fields I6 and I4 respectively for increase or decrease of pitch, when in the positive or normal pitch range. Contacts |46 and |48 complete proper circuits to the fields I4 and I6 for the reverse pitch range.

' The reverse range of pitch adjustment is relatively small compared to the normal or positive range, and an increment of pitch change in reverse or negative pitch produces engine load changes in the order of five fold the engine load change effected by the same increment in the.

positive range. Accordingly, it is desirable to substantially decrease the rate of pitch change or increments of change when in the reverse range. When the latching relay |36 is reversed,

closing contacts |46, |40, and |50, an inter-` 50 time either of the governor relays ||6 or ||||Y close, one or the other of the speed retarder.

rupter relay |22 is brought into action. Each relays |28 or |30 close, placing a potential across the resistor |34, regardless of whether or not a' decrease of pitch is being effected and one of the motor fields is connected to ground therethrough. Whenever contacts |50 are closed, and a` potential exists across resistor |34, the interrupter relay is energized thereby and opens the circuit to the governor contact 34 thereby cutting the iiow of current to the pitch change motor after a momentary flow, to decrease substantially the increment of pitch adjustment.

Thereafter depending upon the time relation the interrupter relay is de-energized by the opening of either relay ||6 or H8, and the consequent opening of the corresponding relay |20 or |30, whereupon the circuit to the governor contact 34 is re-established, and the interrupter Y cycle will repeat, so long as the governor contact 34 contacts one or the other of the contacts 30 or 32.

To effect quick pitch reversal, that is change from the positive or normal range to the negative or reverse range, or vice versa, the hand rection that would effect a decrease of pitch switches |04 or |06 are actuated. Closure of switch |04, opens the battery potential bus 22 through contact |00, and immediately establishes a potential in the series voltage booster relay coil |60, closing contacts |62 to ground to start the booster motor generator |6| to add potential above battery voltage to the booster bus 26 (unless it is already in operation through an auxiliary circuit). At the same time, the lock-in coil |66 is energized, the time delay relay |24 opened, the latching switch relay coil |38 energized, and the pitch change motor and its normal decrease pitch eld I4 energized at high voltage, causing rapid pitch change. When the closes its contacts, thereafter establishing governor control. Return to the normal or positive range, from the negative or reverse range is effected by actuation of manual switch |06, which completes a circuit through its lock-in coil |68 latching relay coil |40, limit switch 42 and the motor I0 through its proper field to produce rapid pitch change into the positive range, when limit lswitch 42 opens. A mechanical or other interlock |10 between the switches |04 and |06 may be provided to prevent accidental actuation of more than one switch at a time.

It may be noted that the time delay relay |24, is only employed to momentarily delay the establishment of governor control in the reverse pitch range until the high speed of the motor can be arrested, this being desirable lin view of the great sensitivity to small pitch changes Within this range, as hereinbefore set forth.

The ranges of normal or positive pitch and re" verse pitch are indicated diagramatically in the circle diagram of Figure 4. The highest pitch in the lowest pitch may be Y2, and the highest pitch may be -l2. In shifting from within one range to the other, the limit switch 40 may be set to cut off at +2", there being about 8 of overtravel before motion can be arrested, to ultimately place the blades at approximately 6 pitch. In the return to positive pitch or normal range, limit switch 42 may cut off at about +35", there being an overrun of about 5, to an ultimate pitch of 40 midway of the range unless the governor calls for a different pitch. It will be understood that the governor is permitted to take over promptly after the limit-switch 42 is opened, whereas governor operation is delayed after limit switch 40 is opened to permit the blades to actually reach 6 and come substantially to rest.

In Figure 3.a cam arrangement with cam followers is shown. Each ofthe cam followers 16, 13, and 82 actuate their respective switches to open their respective circuits when lifted by one or more of the cams. Switch 36 and its follower 16 is actuated by the low normal cam 31 upon clockwise rotation of the cam ring, to limit the lower end of the normal or positive range of pitch adjustment. If the propeller blades are in the reverse pitch range, the high reverse cam 35 will again trip switch 36 and its follower 16 to limit the increase in pitch in the reverse range beyond -12. To place the blades within the reverse pitch range, the cam ring will rotate clockwise until the reverse cam 39 trips the .switch 40 and its cam follower 80. Cams 35, 31 and 39 are on the lower flange 68 and the cam followers 16 and y counterclckwise rotation-.ofthecamzringwvillbe? 5.'

ellected'guntii;camv 43 tripsesxvitchillzfrthrougli its:l follower. 82;. li'urtherrcounterclockvseerotation*r Willjoring thefbladeipitchztorthe highfzpitch limitg. causing. cam ,451i to 3- trip switch'. 33 vthroughiitsi follower. :'18s Il'r thezrelationeshown; switch .38510' has; been trippedand: there-` h'asfz occurredfsome. overrun; Cams 41s ,43vandg45 areslcatedfupone the uppergiiangeaa andxthezcam followers v'I 8 and; 8.2;of;switches;3Bpandd2.are:-1ocated,intcoeplanarr rclatiomtherevvitmz.

In practice; thezboosterfvoltageeis' :suiiicientvto: shift :thefpitchjrommnezrange toxthegother inta: factionsof aeseeondgand -With;th`e:aid zofs'countere'- Weightsrto :compensate for a. portiorriory al1 of :the 1 centrifugal twisting amoment, thee. gearf'reduction 20 ratiorbetweerrmntor and blade gear .maya be less; than 1000:-1A to: assist faster# action; It Wil] .be. appreciated thaththelocation of thesgcams `may be.Y varied .to suit conditions; andithat inzilo eating the cams, .the gear V'ratio between .thermasten geerrlllir 25.

andfbladegears mnstbertaken intoraccountx'.

From theforgoing'itwi'll be seerr that :fast con.;V trol: overgthefthrust characteristicsl vof a:propellerf maybe had toitheendfth-at full enginepowerzmayr be: almost'finstantlw appli-ed;I either f tof provide 30 tractiver-eiort or brakingeiort,A atr theawillof the pilot, and through a'simple'handiswitch control. By thesimple expedient; for example, .of "operating the; hand switch |04, governorv controlled 're-- versethrust may be established-Within. arsplit35 second;

Though a singleaembodimentsof, the linventionv has. been :illustrated -and describedsiby: 'an electric circuitand associated means, it--isf to beunderJ stood that the inventioni may be :embodied in 40 various equivalent arrangements:Variouschanges and substitutions may be made, Without depart-v ing'from thespiritof the invention as'will be: apparent to those skilled inthe art-and referenceY should therefore-be had to the'appendedclaims@- for a definition of the vlimits ofthe invention:

What is claimed-"is:

1. In ank electric variable pitch propeller; a1L source'of low potential; asource of high potential, a reversible pitch changing motor'connectableat 5 times to eithersource,V switch means responsive to blade position forestablishing' and 'breaking cire.- cuits to said motor, saidE Ineensestablis'hing a' rangel of positive pitch adjustment;V arrange of* negative 'pitch adjustment; and "a" range effective toshift the blade positionfromy one *to the` otherVlv ofi the rst andlsecondnamedranges; a' speed responsive governor 'to energize saidl :motor from Y saidlow vpotential Vsource for operatiorri'n one'direction or the other, means -actuatedfb'y-position- 60 ing of thepropeller blades in- -the'negatve pitch range tovreduce'the energysupplied to said motor'VJ by voperation lof said governor, meanssimultaneously operable to connect said motorV to said' sourcev'of high potential, to disconnect said gov-65 ernor transiently and toreverse theconnections of rsaid governor to thereby cause the blade posi--u tion to traverse'said last namedrange and thereby shift from one to the other of said first named ranges, and means actuated-by attainment `of' the 70 other rangeto reconnect said governorland todis-A connect said high potential source:

2; Ina variable pitch propeller; ahub', blades swivelly mounted therein for vpitch Variation, af variablelspeed electric motor for.` alteringythe 75 p itchzof; saidzbladess.at;l sources ofjpovver;l speed; governor .-meansgconnecting fsaidsource Ofzppwerr tof..said1fmotor; to eiect-I chaneesgof p itch raina-E. nominal rate .inthe forwardpitchrange;.means for increasinggthe;pptentialcf.;saidasourcc ots. powergfandy for.` applvngrsaid increased pptential. to said motor tofreverse the pitch; or. the :propeller-r'.- atL aahigher'; thanrnominal rate,A means for; es=-4 tablishing` gpvernor connections -toL said .-motorrin: reversed; sensec upon... completion; of; the pitchY reversa-1,.- andmeansrcomprising ai pulsing `winter.:n rupterV .in the--.reverse.-.sense: governor-w, connectiom to. decreasethe :speed :of .said motor tdeect fgpv ernoncontrolled changes-,of p itch .in the. reverse.- pitch range at less than nominakrate-s.

3:: InL a; variableepitchy propellenfa humble-des swivelly; mounted fthereinlfor.V p itcln,variationsaev reversible. electricmotor.: for altering thepitchs of said blades having forward andreverseffields-e each serially "connected 'with Aan armature,:means..A

for .separatelyvenergizingL said elds for .changingr pitclnandA .for concurrently f shuntingl the other: ield. in parallel .with .said Larmature` throughv .-.a-.-. resistor Vto .increasethefield strength, a governors. means actuated.. thereby for.; controllingV saldi. energizingmeans, means ,to operatesad. motor.; forreversing the pitch of. thepropeller.blariesi.L means for. reversing. thel y.sensecof the f governor... actuatedby said operating, meansf and relay,l means connected into :the energizing. means .cire .L cuit AWhen the .-propelleris. reversed ,tor periodical:- ly interrupt said. energizingl means for..decrcas: ing theV rate of .pitch..changel,

4.. In avariable pitchpropeller,including lahub. and blades mounted. thereinior pitch. .changingm reversible pitch changing.Y mechanismconnected, tosaid. blades .to changethe pitch thereof, rneansA to energize said mechanism to operateratselece.- table .highrintermediate-,- andlow. rates. of pitch change, apitch range. selectoradj 1 ist'able.tQselectlK normal.. positiver pitch or reverse .pitch means., actuated. byy adjustment.. of the selectorI from.. normal to. reversepitch. and from .reverse pitch.. to .normal .pitchto energize said mechanism ,.for.. high..rate :ofptchchange .only for the ,periodref 0 quired by the .blades to make..the.transition from.;

one range .to the, other, .means actuatedbyad:

justment ofthe selectorinv the.normalpositiven range and actuated also by the positioning ofthe. blades inthe normalpitch range toenergizesaidj.

0 mechanism for operation atintermediate-.rate of;

pitch change, and means actuated. byy adjust ment of vthe .selectoninv thereverse pitch'. range andactuatedlalso bythe positioning gofjhelbladese in .the .reversepitch rangeto energizesaidmeclif anism..for operation. at. the- 10W rateoof...` pitch'. change.

5T Mechanism according to claim 4..-wherein.- said means toV energizefor.highlrate ofjpit'rh; changeincludes ,devices to `overridesaid. lovv andi medium' rate means during lpitch transitiomandl to'yield'control 'of pitch change rate tosaid other, means upon completion ofApitch.transition` 6." Iny a variablepitch propeller, ahub,. blades. mounted therein for pitch change, motormeans. connected to saidbladesoperable toalterblad, pitch, said motor means beingzoperab'le athgh;. intermediateandlow'speeds to change blade pitch. at'diiferentLrates, blade'pitch limit stops intheA motor means-blade connection identifyingkrnormal and reversey blade pitch" ranges. governor means selectively connectible to'themotorrmeans; to operate the motor means at an intermediate speed; a selectorfor propel-ler operation in the. normal pitch range, means actuated@ by" saldiv selector-to `connect said governor; said motorrand'* said operating means together enabling governed propeller operation in the normal pitch range at intermediate rate of pitch change; a selector for propeller operation in the reverse pitch range, means to operate the motor means at a low speed, and means actuated by said reverse selector to connect said governor in reverse sense, said ioiv speed operating means and said motor means for operation in the reverse pitch range at a low rate of pitch change.

7. In a variable pitch propeller, a hub, blades mounted therein for pitch change, motor means connected to said blades operable to alter blade pitch, said motor means being operable at different speeds to change blade pitch at different rates, blade pitch limit stops in the motor meansblade connection identifying normal and reverse blade pitch ranges, governor means selectively connectible to the motor, means to operate the motor means at an intermediate speed, a selector for propeller operation in the normal pitch range, means actuated by said selector to connect said governor, said motor and said operating means together enabling governed propeller operation in the normal pitch range at intermediate rate of pitch change; a selector for propeller operation in the reverse pitch range, means to operate the motor means at a low speed, means actuated by said reverse selector to connect said governor in reverse sense, said low speed operating means and said motor means for operation in the reverse pitch range at a low rate of pitch change; means to operate the motor means at a high speed, and means actuated by the normal and reverse selectors when the propeller is in the reverse and normal ranges respectively which transiently connects the motor to said high speed motor operating means in sense to change propeller pitch respectively from the reverse pitch range to normal pitch range, and from the normal pitch range to the reverse pitch range at a high rate of pitch change.

8. In a variable pitch propeller having a |hub, blades mounted therein for pitch change and an electric motor connected to the blades, a power supply having a normal steady voltage output, connectible at times to the motor to operate same for an intermediate rate of pitch change, a booster circuit driven by the power supply having a steady high voltage output ccnnectible at times to the motor to operate same for a high rate of pitch change, an interrupter circuit connectible at times to the motor, energized by the power supply and including a pulsing interrupter to pass an average amount cf power substantially less than that provided by the power supply alone, connectible at times to the motor to operate same for a low rate of pitch change, and means selectively operable to connect to said motor either said steady power supply, said booster circuit or said interruptor circuit.

9. In a variable pitch propeller having a hub, blades mounted therein for pitch change and an electric motor connected to the blades, a power supply having a normal steady voltage output, connectible at times to the motor to operate same for an intermediate rate of pitch change, a booster circuit driven by the power supply having a steady high voltage output connectible at times to the motor to operate same for a high rate of pitch change, an interruptor circuit connectible at times to the motor, energized by the power supply and including a pulsing interruptor to pass an average amount ci power substantially less than that provided by the power supply alone, connectible at times to the motor to operate saine for a low rate of pitch change, means in said propeller establisning a normal positive pitch range, means in said propeller establishing a negative pitch range; and means to connect said steady power supply to said motor for operation oi the propeller in the normal pitch range, means to connect said interrupter circuit to said motor for operation of the propeller in the reverse pitch range, and means to connect said booster circuit to said motor for operation of the propeller from the forward to the reverse pitch range and vice versa. 10. In a variable pitch propeller, a hub, blades mounted therein for pitch change, a reversible electric motor connected to said blades for altering the pitch thereof, a power supply selectively operable to energize said motor for increasing and decreasing blade pitch in the normal positive itch range, limit switches defining the limits of said normal positive range, power augmenting means -driven by said power` supply, means selectively operable to operate said augmenting means and to connect it to said motor for driving the motor at high speed from positive pitch range to negative pitch range and vice versa, said selectively operable means including circuit switching to override said limit stops and to disconnect the power supply from the motor when the augmenting means is connected thereto, limit stops dening a negative pitch range, one of said stops being connected in the circuit of the motor and augmenting means to break that circuit when the blades have been driven to the reverse pitch range by the augmenting means, another circuit energized by said power supply and including a pulsing interruptor operable when the other circuit is closed to decrease the average power supplied through said other circuit, and means to connect said other circuit to the motor when the blades are in the reverse pitch range after said augmenting means has relinquished energization of said motor.

WILBERT W. FRANK.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,076,202 Lewellen et al Apr. 6, 1937 2,293,912 Mullen Aug. 25, 1942 2,346,007 Chillson Apr. 4, 1944 2,378,938 McCoy June 26, 1945 2,388,276 McCoy Nov. 6, 1945 2,410,630 Chilman Nov. 5, 1946 2,426,007 Forsyth Aug. 19, 1947 2,455,378 McCoy Dec. 7, 1948 

